1. Field of Invention
The present invention relates to a media processing device that reads contained information such as magnetic ink characters and image information from sheet media such as checks while conveying the media one at a time through a transportation path, and relates more particularly to a media processing device that can suppress fluctuations in the sheet media transportation speed so that the contained information can be accurately scanned.
2. Description of Related Art
Banks and other financial institutions use check readers to image and read magnetic ink characters from checks, promissory notes, and other check-like negotiable instruments, and to sort the checks based on the acquired information. As electronic check processing has become more common in recent years the scanned image data and magnetic ink character data is also processed and managed using computers. See, for example, the check readers taught in Japanese Unexamined Patent Appl. Pub. JP-A-2004-206362, U.S. Patent Application 2004/025626, and Japanese Unexamined Patent Appl. Pub. JP-A-2001-48362.
Separation mechanisms for separating and feeding multifed checks and other sheet media one by one for processing include pad separation devices and retard roller devices. Pad separation devices push the end part of the sheet media against a separation pad that is made from a material with a high coefficient of friction while driving a feed roller to separate and feed one sheet medium. Retard roller devices separate the sheet media by passing the media between a media feed roller and a retard roller, which is pressed against the media feed roller and applies a rotational load. Both methods create resistance to the transportation direction of the sheet media being fed in order to separate multifed sheet media one by one in the transportation direction.
Japanese Unexamined Patent Appl. Pub. JP-A-2001-48362 teaches a sheet supply mechanism for separating and supplying high rigidity sheet media one by one. This sheet supply mechanism rotatably supports a separation pad so that the contact surface of the separation pad tightly contacts the end of the sheets supplied from inside a cassette case, and prevents sheets from being supplied in a stack to the retard roller type separation roller.
The transportation mechanism for conveying sheet media fed that are fed one at a time through a separation mechanism as described in Japanese Unexamined Patent Appl. Pub. JP-A-2004-206362 and U.S. Patent Application 2004/025626 transfers torque from a transportation motor through an intervening endless belt to a plurality of transportation rollers disposed along the transportation path, and sequentially conveys the sheet medium from an upstream-side transportation roller to the next downstream-side transportation roller along the transportation path.
If the check speed is fast, if the coefficient of friction between the check and the transportation roller is low because the check surface is particularly smooth, for example, or if the check transportation load is high, a certain small amount of slippage between the transportation roller and check occurs even if the relay capacity (μF) of the transportation roller is increased. If the check being conveyed slips while information is being read by the magnetic head or scanner, the reading accuracy of the information drops because of fluctuations in the transportation speed.
Furthermore, because the separation mechanism separates the media by applying a resistance to the transportation direction, the transportation load when conveying a check varies greatly depending on whether a part of the check is still inside the separation mechanism or whether the check has completely passed the separation mechanism and no part is still inside the separation mechanism. The check causes this variation in the transportation resistance of the separation mechanism to directly affect the transportation roller that receives and conveys the check from the separation mechanism to the scanning position of the scanner, for example. This produces slipping between the transportation roller and the check, which causes the speed of the check to vary as it is conveyed while being read by the scanner, for example, and can result in a drop in scanning precision and reading accuracy.
The nipping pressure (F) applied by the transportation roller to the check must be increased to increase the relay capacity of the transportation roller in order to reduce slipping of the checks conveyed by the transportation roller. However, this requires a design change, such as increasing the strength or rigidity of the transportation roller support shaft, which increases device size. Furthermore, because the required relay capacity of the transportation roller is affected by the coefficient of friction between the transportation roller and the surface of the check, differences in the condition of the check surface cause transportation roller slippage to vary. This causes the transportation speed to vary from check to check and reduces the reliability of information read from the checks.